1. Technical Field
The present invention relates to the technical field of machining and particularly to the field of non-traditional machining processes and equipment employing the techniques of and compositions for abrasive flow machining, grinding, deburring, radiussing, leveling and polishing of work pieces. Such processes are typically employed in the working of castings, forged parts, machined parts, and the like. Most often metal parts and the like. The present invention particularly relates to such operations where the flow is attained by relative motion, preferably orbital motion, between the work piece and the abrasive medium.
2. Prior Art
Abrasive flow machining has gained wide acceptance for a number of applications as the machining and finishing technique of choice. Such techniques are particularly adapted, for example, to working interior passages in work pieces, for light grinding, deburring, radiussing leveling and polishing of complex surfaces, and particularly three-dimensioned surfaces where surface detail requires working, and in repetitive working of multiple work pieces of complex form and shape.
In its simplest form, abrasive flow machining requires passing a visco-elastic medium containing an abrasive across the surfaces to be worked. The visco-elastic medium functions as a carrier for the abrasive, and transmits working force to the abrasive as the abrasive is carried across the surface. the medium flows to conform to the surface of the work piece.
In many contexts, advantage is taken of the visco-elastic character of the medium to pump the abrasive filled medium through passages, across surfaces, and between a work piece surface and a suitable member to confine the flow and constrain the medium in engagement with the surface of the work piece.
In many contexts, particular advantages are attained when the visco-elastic abrasive medium is also rheopectic, i.e., increasing in apparent viscosity with applied stress. (The behavior of rheopectic materials is. in essence, the converse of thixotropic behavior.) With the appropriate application of stress, typically either shear or compressive stress, to the medium, it is possible to substantially attain plug flow of the medium across the surfaces of the work piece to be worked in the operation. Substantially higher working force is applied to the surface by such plug flow when compared to viscous flow of the medium.
A more detailed description of the basic prior art on orbital abrasive flow polishing and grinding can be found in U.S. Pat. Nos. 3,521,412, 3,634,973, McCarty and U.S. Pat. No. 3,819,343, Rhoades.
One particularly attractive implementation of abrasive flow machining has been the employment of an rheopectic visco-elastic abrasive medium in combination with an orbital drive mechanism, where the medium and a work piece are confined together in a pressurized chamber with a "displacer member" generally conforming to the inverse of the shape of the work piece surfaces to be worked, and where the orbital motion of the work piece relative to the chamber displacer member and the contained medium causes the work piece to be effectively worked. Such operations take advantage of the ability of the medium to conform to the surfaces of the work piece, and even complex, highly detailed surface shapes can be worked with considerable success and effectiveness. See U.S. Pat. No. 5,125,191, Rhoades.
It is in the context of such abrasive machining to which the present invention particularly relates, although the considerations disclosed and described herein may have broader and more general applicability in specialized circumstances.